Interactions Intramolécularies—XVII Calcul des constantes de couplage en RMN du cyclohexane et de cyclohexanes substitués. Comparaison des méthodes de Pople et Santry et des perturbations finies

Proton–proton ³J, ⁴J and ⁵J NMR coupling constants have been calculated for cyclohexane and monosubstituted cyclohexane conformers (substitiuents: Li, CH₃, OH, F) by the two methods mentioned. Comparing the two methods on the basis of group theory, we show the necessity to use the second. The results from this method are compared with those of the literature.     

Dosage de traces d'hafnium dans l'aluminium par activation neutronique

Three methods are proposed for the assay of traces of hafnium in aluminium metal by neutron activation analysis. In the first method, the isotope ^179mHf (T = 19 s), produced is counted after anionic resin exchange-separation in sulfuric acid medium. The two other methods, which are non-destructive, are based on the formation of ^180mHf (T = 5,5 h) and ^179mHf (T = 19 s). The latter method comprises an instrumental separation.     

Utalisation des deutons et des tritons de faibles energies pour le dosage du carbone et de l’oxygene presents a la surface d’echantillons metalliques

The oxygen and carbon concentrations on metal surfaces were determined by two methods. The first method was based on the detection of the emitted particles in the¹²C(d,p)¹³C and¹⁶O(d, p)¹⁷O reactions, the second one on the measurement of the induced radioactivities in the¹²C(d,n)¹³N and¹⁶O(t,n)¹⁸F reactions, respectively. The results, obtained by the two different methods for high purity metals, were in agreement. A type of error which exists in the determination of trace amounts of carbon and oxygen in pure metals by combustion and reductive fusion was quantitatively demonstrated. This error exists also in the determination of oxygen by 14 MeV neutron bombardment.      

Sur quelques nouveaux oxyfluorures de structure rutile

Transition metal oxyfluorides with rutile structure have been obtained by various synthesis methods: NiM′³⁺TiO₃F₃, CoM′³⁺TiO₃F₃ (M′³⁺ = V³⁺, Fe³⁺); NiVTiO₄F₂, CoVTiO₄F₂ and NiCoTiO₂F₄. Electric and magnetic measurements indicate a semiconducting and antiferromagnetic behavior.     

Synthese regioselective de bases de mannich de cetones dissymetriques

Methods for the regioselective synthesis of Mannich bases starting from unsymmetrical ketones are described. The Mannich base on the more substituted carbon is obtained by reaction with (CH₃)₂N⁺CH₂,CF₃CO₂^- in CF₃CO₂H and its isomer on the less substituted carbon with (iPr)₂N⁺CH₂,ClO₄^- in CH₃CN. In the first case, the orientation corresponds to a non-selective attack of the immonium salt on a mixture of enols in which the more-substituted isomer is predominant. In the second ease, use of a bulky immonium salt induces a selectivity favoring the less-substituted enol.     

Analyse isotopique de l'azote par spectrometrie optique,pour de faibles teneurs en 15n

For mixtures of ¹⁴N₂ and ¹⁴N¹⁵N low in ¹⁵N (isotopic abundances less than 2%), previous optical spectrometric methods do not produce rapid results of sufficient precision. In this paper, operating conditions are described for the determination of the isotopic content to ±3% near the natural abundance and to ±1% when the sample contains an atom ratio of ¹⁵N: ¹⁴N of 1.5:100. The time required for a determination is ca. 10 min. A spectrometer is modified by the substitution of an exit slit and a photomultiplier in place of a photographic plate. The excitation of the electrodeless discharge tube is made by a high-frequency field. The method has been applied to samples of ammonium salts, fertilisers and plant material. In all cases, the precision of the isotopic measurements was greater than that required for most agricultural studies (5–6%).     

Détermination de la structure cristalline du ferrite de baryum Ba2Fe6O11

The crystal structure of dibarium triferrite Ba₂Fe₆O₁₁ has been solved by direct methods, using intensity data collected by means of an automated diffractometer (MoKα radiation) and corrected for absorption. It crystallizes in the orthorhombic space group Pnnm: a = 23.024(10)Å, b = 5.181(3) Å, c = 8.900(4) Å, Z = 4. Program MULTAN was successfully used for locating Ba²⁺ and most of the Fe³⁺ ions. The structure was further refined by conventional Fourier and least-squares methods (full-matrix program) to a final R value of 0.045 for 1448 observed reflections. Fe³⁺ ions occur in both octahedral (FeO mean distance: 2.02 Å) and tetrahedral (FeO mean distance: 1.865 Å) coordination. Two types of Ba²⁺ ions are found, with six and seven neighboring oxygen atoms. The structure consists of sheets of edge-shared FeO₆ octahedra which are connected by means of corner-shared tetrahedra.     

Structure de la couche double sur les électrodes d'or: Détermination des composants de charge

The components of the charge q_±^Au at the interface polycrystalline gold electrode—NaF, KCl or KBr solutions and the charge due to specifically adsorbed Cl^? or Br^? anions have been determined by thermodynamical analysis of differential capacity—potential curves, using the two sets of variables q^M, μ (Grahame and Soderberg's method) and E_?, μ (Esin—Markov effect). In the absence of specific adsorption (NaF), variations of charges q_±^Au with potential are in good agreement with those provided by the diffuse layer theory in the negative charge region of the metal. With specific adsorption of Cl^? or Br^? anions, both q_±^Au(q^Au), (q_?¹)^Au(q^Au) curves obtained by the two methods fit well. Determination of components of charge was made in the whole negative charge region and in part of the positive charge region of the electrode.     

Modelisation de la reaction chimique de durcissement d'un systeme epoxy

Chemical, as well as spectroscopical methods, were used to try to describe, as quantitatively as possible, the different kinds of chemical bonds constituting the network of a cured epoxy matrix, the tgmda/ DDS system. The chemical approach consisted, on the one hand, in synthesizing model compounds; on the other hand, model reactions from diepoxy and amino compounds were followed by chemical, chromatographical and spectroscopical analysis, in order to correlate structure of the products with reactivity of the starting molecules. Spectroscopical method, which was found most useful for this resin system, is solid state ¹³C CP/MAS NMR spectroscopy. As the spectra were not directly interpretable, because consisting largely of broad, bad-resolved peaks, the aliphatic carbon region was decomposed into elementary lines. Structural assignments of the latter were made by using the solution state ¹³C NMR data of model compounds. On account of the anticipated mechanisms, 85 % of the aliphatic carbons could be identified and quantified.     

Sur de nouveaux borates mixtes des métaux de transition isotypes de la warwickite

The isomorphism of borates CaLn³⁺BO₄ where Ln³⁺ stands for a small rare earth cation of Y³⁺, with the mineral warwickite (Fe,Mg)₃Ti(BO₄)₂ is demonstrated. The octahedral sites of the warwickite structure seem thus to accommodate rather large cations, like trivalent Y³⁺ or Dy³⁺ and bivalent Ca²⁺. The synthesis of several new transition-metal borates with this structure is reported. From a survey of all the warwickite-type compounds one comes to the conclusion that the structure is only stable when the size of the divalent cation M²⁺ is larger than that one of the trivalent M³⁺.     

Etude des possibilites de dosage du lithium par activation au moyen de protons et de deutons de moyenne energie

The determination of lithium by measuring⁷Be, produced by proton or deuteron activation, has been studied. The extent of interference from boron or beryllium, which also form⁷Be, was measured. The calculated sensitivity limits when activating for one hour with 10μA beams of 14 MeV protons or 25 MeV deuterons are, for lithium, 1·10⁻¹ and 2.5·10⁻² ppm and for boron, 2·10⁻¹ and 1·10⁻¹ ppm, respectively.      

Ionisation et Fragmentation en Spectrométrie de Masse. VI—Energie d'Activation de la Fragmentation Principale des Monohalogénobenzènes

The activation energy of the fragmentation [C₆H₅X?]⁺ → [C₆H₅]⁺ + X? (X = Cl, Br, I) is calculated by various methods. These results are compared with determinations of kinetic energy release and with rate constant values available in the literature.     

Structure de benzoates de fluoroalkyles

The crystal and molecular structure of 2,2,3,3-tetrafluoropropyl-parachlorobenzoate (C₁₀H₇ClF₄O₂) has been determined by X-ray diffraction. The crystals are monoclinic, P2₁, a = 4.826(1), b = 9.036(2), c = 12.442(4)Å, β = 94.64(2)°, V = 540.8 ų, Z = 2, D_x = 1.66 Mg m^?3. Starting from the ¹³C data of this compound, the identification of five other fluoroalkylbenzoates has been achieved by N.M.R. spectroscopy.     

Fabrication de128Xe comme traceur pour l'analyse de traces de xenon

¹²⁸Xe is produced by one-day irradiation of potassium iodide at a neutron flux of 10¹³ n·cm⁻²·s⁻¹ at a rate of 0.9 mm³ TPN for one gram of iodine. Xe is separated from the matrix by melting or hydrolysis. The main part of water is removed from the gas by cooling. Xenon (∼99%) thus obtained is freed from H₂, O₂, N₂, CH₄ and the last traces of water by gas chromatography and used for isotopic analysis.      

Etude par thermogravimetrie,analyse thermique differentielle et spectrographie d'absorption infra-rouge de la reaction du peroxyde de sodium sur l'oxyde de Beryllium

Thermogravimetric and differential thermal methods as well as chemical analysis show that sodium peroxide attacks beryllium oxide to form beryllate, apparently in the molecular ratio 1 Na₂O:1 BeO. An unidentified peroxy compound of beryllium is formed at about 165° by the action of the NaO² present in the Na₂O₂ sample; it decomposes between 280 and 310°. IR absorption spectroscopy indicates the presence of Be-O bonds in the sodium beryllate which are different from those in the oxide used.     

Détermination colorimétrique de l'Iode sous forme de triiodure de Nitrone

Résumé Etudiant l'action mutuelle du nitron (Nt) et certains complexes halogènes on a obtenu le composé NtI₃. On a établi les propriétés, la composition et le mécanisme de la formation du composé. Ses propriétés ont servi de base à l'élaboration d'une méthode d'extraction et de détermination colorimétrique de microquantités d'iode. La méthode est basée sur l'oxydation de I^– en IO₃ ^–, réduction de ces derniers à l'aide de I^– en milieu acide et obtention de I₃ ^–, qu'on extrait sous forme de NtI₃ à l'aide de C₂H₄Cl₂ en presence de NtHSO₄. La méthode peut être mise à profit en présence de SO₄ ^2–, Cl^–, Br^– et NO₃ ^–.Cette méthode permet la détermination de 2 à 20g d'iode, dans 25 ml de solution, le coefficient des variations étant de ±3%. On s'est servi de cette méthode pour déterminer l'iode dans des eaux de sondage.

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Fluorimetric determination of iodine in the form of nitron triiodide

Summary The compound NtI₃ has been obtained by studying the mutual action of nitron (Nt) and certain halogenated complexes. Its properties have been established, also its composition and the mechanism of the formation of the compound. Its properties have served as the base for the elaboration of an extractive method for the colorimetric determination of microquantities of iodine. The method is based on the oxidation of I^– into IO₃ ^–, reduction of the latter through I^– in acidic surroundings and obtaining I₃ ^–, which is then extracted in the form of NtI₃ with the aid of C₂H₄Cl₂ in the presence of NtHSO₄. The method may be employed to advantage in the presence of SO₄ ^2–, Cl^–, Br^–, and NO₃ ^–. This method permits the determination of from 2 to 20g of iodine in 25 ml of solution, the coefficient of variation being ±3%. The procedure has been used to determine the iodine in boring waters.

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Zusammenfassung Bei der Einwirkung von Nitron (Nt) auf gewisse Halogenkomplexe wurde die Verbindung NtJ3 erhalten, deren Eigenschaften, Zusammensetzung und Bildungsweise untersucht wurde. Sie eignet sich für die Extraktion und kolorimetrische Bestimmung von Mikromengen Jod. Jodid wird zu Jodat oxydiert, dieses in saurer Lösung mit Jodid reduziert und das dabei entstehende J3^– als NtJ3 mit Dichloräthan in Gegenwart von NtHSO₄ extrahiert. Das Verfahren ist bei Anwesenheit von Sulfat, Chlorid, Bromid und Nitrat anwendbar und eignet sich zur Bestimmung von 2–20g Jod in 25 ml Lösung mit einem Variationskoeffizienten von ±3%. Es wurde für die Jodbestimmung in Brunnenwasser verwendet.

     

Etude de la conductivite anionique dans quelques fluorures amorphes obtenus par hypertrempe

Fluoride ion conductivity has been investigated in amorphous materials obtained in the BaF₂-ZnF₂, PbF₂-ZnF₂ and BaF₂-MnF₂ systems using both NMR and complex impedance techniques. The activation energies appear to be about 0.53 eV with a good agreement between both methods. Ionic conductivities have been found to be larger than 10^-5ω^-1cm^-1 at 180°C, values which are among the best ones so far obtained for fluorine conducting glasses.     

Determination par calorimetrie de dissolution des enthalpies de formation de quelques silicates,aluminates et alumino-silicates de calcium

The enthalpies of formation of 13 calcium silicates, aluminates, alumino-silicates and ferro-alumino-silicates were measured by dissolution calorimetry with the help of a high-temperature Calvet calorimeter. Dissolution experiments were performed in a lead metaborate (2PbO?B₂O₃) baths at 1173 K. The synthesis of the samples was realized by melting together pure silica, alumina, ferric oxide and calcium carbonate in appropriate ratios. The samples obtained in this way were examined by X-ray diffraction and scanning electronic microscopy. The free lime content was also determined by chemical analysis. The enthalpy of formation of silicates and aluminates obeys two different linear relations with respect to the ratio Ca/X (X=Al or/and Si) except for Ca₁₂Al₁₄O₃₃ which does not exist in its pure form but has to be stabilized by anions as OH^? or Cl^?. The data corresponding to the two aluminosilicates are located between these lines. The enthalpy of formation of tricalcium silicate (Ca₃SiO₅ i.e. C₃S according to the Bogue terminology) from dicalcium silicate and lime could be calculated as ?6kJ·mol^?1. This reaction is the most important one in the industrial process of clinkerization.     

Obtention de phosphore élémentaire et de phosphures de nickel par électrolyse de solutions de pentoxyde de phosphore dans des bains à base de cryolithe

By electrolysis of cryolitic solutions of P₂O₅, elementary pure phosphorus is obtained on carbon cathode and Ni phosphides on Ni cathode. The most probable mechanism of phosphorus formation in these conditions seems to be the final dissociation of P₂O₅ in P⁵⁺ and O^2? and the primary electrodic discharge of these ions.     

Modele de nitrogenase. activite de complexes molybdenecysteine dans la reduction de l'acetylene

The complex Mo₂O₄(cys)₂^2? disproportionates nito Mo^VI and Mo^III at a _pH higher than 9. Under our experimental conditions, the reduction of acetylene by molybdenum-cystéine complexes does only occur after addition of naBH₄·Mo^III; the molybdenum(III) species seems to be responsible for this activity.